The present invention relates to an image processing method in which image information is inputted by reading an image from an original document by a scanner or the like, for example, is subjected to predetermined image processing such as gradation correction or the like, and is thereafter outputted onto a paper sheet by a laser printer adopting an electronic photographing method, as well as an image processing apparatus such as a digital copying machine which uses the image processing method.
In general, in an image processing apparatus such as a digital copying machine dealing with image information, image information is read from an original document by a reading means such as a scanner or the like, converted into multi-value information, and digitized image information is processed in compliance with purposes and is outputted from an output means such as a laser printer or the like. This kind of apparatus has a density correcting function of automatically correcting the density in compliance with the original document without correcting the density by a density adjust button when the image information read by the scanner includes a background portion of the original document or characters on the original document are light in color.
Recently, as one of the density correcting function, a method has been proposed in which a density histogram is formed from inputted image information and the kind of an original document (or the kind of image information) inputted is decided from characteristic amounts concerning the density histogram, thereby to correct the gradation of the inputted image information in accordance with the decision result.
In order to correct the image density with use of characteristic amounts concerning an original document, it is important to exactly decide the kind of the original document (or the kind of image information). However, original documents includes a kind of character original document (or a character image), a kind of photographic original document (or photographic images), and others kinds of which cannot be easily decided, e.g., an original document including characters and pictures mixed therein, an original document including different kinds of backgrounds together, an original document including light-colored characters and deep- colored characters mixed therein, etc. Thus, there are many kinds of original documents which cannot be processed equally by only one data form, i.e., many original documents cannot be decided with respect to their kinds.
Particularly, for example, magazines often show such a photograph original document D as shown in FIG. 23, which includes a white band portion W1 having a density close to white in the periphery and characters having a background W2 surrounded thereby, as well as another background B having a color density deeper than the back ground W2. Note that P1 and P2 in FIG. 23 respectively denote a character image and an image other than characters.
This kind of original document, however, often cannot be recognized correctly, and the density of such a portion which needs to be reproduced is also often deleted. For example, in case where image information is obtained by reading the original document D shown in FIG. 23, the image density of the image information is corrected by the method described above, and is thereafter outputted in form of a hard copy by a laser printer. Consequently, an output image D' also shown in FIG. 23 is obtained, and a portion corresponding to the background B in FIG. 23 is not reproduced but deleted, as can be known from the example of the image D'.